Ore-forming Fluid Evolution And Ore Genesis Of The Dahutang Tungsten Polymetallic Ore Field In Jiangxi Province, China

The Dahutang tungsten polymetallic ore field is located north of the Nanling W–Sn polymetallic metallogenic belt and south of the Middle-Lower Yangtze River Valley Cu–Mo–Au–Fe porphyry-skarn belt?MLYRB?.In terms of tectonic position the ore field lies to the north-central of Jiangnan Proterozoic arc zone of Yangtze Craton.It is a newly discovered ore field,and represents the largest tungsten mineralization district in the world.The ore field has an estimated tungsten resource of up to 2.0 million tons of WO₃ and an established tungsten reserve that exceeds 1.1million tons of WO₃ and 0.6 million tons of copper and molybdenite.Although the geology and the geochemical characteristics of tungsten deposits in the Nanling and surrounding area have been well studied,little is known about the new proved tungsten deposits like Dahutang and Zhuxi in the south of the MLYRB.Given this,under the guidance of geological prospecting prediction theories,this paper presents new tectonic settings,microthermometric,geochemistry and isotopic studies of fluid inclusions in quartz from different ore-forming stages of the Shimensi tungsten deposit in the Dahutang ore field.The significance of the research results is discussed in terms of ore genesis and its usefulness as a reference for further exploration in the study area.Based on these studies I get some understanding as follows:?1?The Shimensi deposit and the Shiweidong deposit in the ore field are the pruducts of a same tectonic-magma-mineralization setting and the development of cryptoexplosive breccia or not is the important reason for the difference of resource reserves between the two deposits.?2?The geochemical analyses suggest the pegmatoid is a crystallization product of the Yanshanian magmatic rocks.The melt and melt-fluid inclusions were found in quartz from pegmatoid bodies mainly composed of Si,K,Na,K,Ca,W,and Sn.The results indicated the fluids were mainly derived from Yanshanian granitic magma and the pegmatoid can be approximated the starting point of the fluid evolution.?3?The most important type of fluid inclusions in quartz from various stages of the Shimensi deposit is liquid-rich two-phase fluid inclusions.The homogenization temperatures of these fluid inclusions range from 162 to 363°C and salinities are0.5–9.5wt.%NaCl equivalent.The ore-forming fluids can be approximated by a NaCl–H₂O fluid system,with small amounts of volatile components including CO₂,CH₄ and N₂,as suggested by Laser Raman spectroscopic analyses.The C–H–O isotopic data are interpreted to indicate that the ore-forming fluids are mainly composed of magmatic water in the early stage,and meteoric water was added and participated in mineralization in the late stage.Immiscibility with the melt,cooling of the ore-forming fluids and mixing with meteoric water may be the key factors that led to mineralization in the Dahutang tungsten polymetallic ore field.?4?The formation of ore field is closely related to the special compression changed to extension geodynamics background of the MLYRB.The upwelling asthenosphere led to partial melting of the Shuangqiaoshan Group which rich in W and Cu to form the highly fractionated S-type granite magma in Yanshanian,and the granite magma reacted with the high CaO granodiorite that promoted the veinlet–disseminated scheelite mineralization.In addition,a strong crust-mantle interaction caused the ore field have more mantle-derived components in terms of ore-forming material sources than the Nanling tungsten deposits.?5?This paper identifies the Yanshanian granite porphyry is the metallogenic geological body of the tungsten and copper mineralization,and it is also have the potential to prospecting the Ni–Ta ore body in the deep.?6?Based on above results,this paper studies the metallogenic geological body,metallogenic structures and structural plane,metallogenic characteristics,and constructed a primary"geological prospecting prediction model"of the Dahutang tungsten polymetallic ore field.